Direct Drivers for LED lamps are popular for their low cost, low EMI and high efficiency. The general operating principle of these low voltage LED direct drivers is that they are able to reconfigure the overall number of LED diodes in a large LED string. The number of powered LED diodes, with a proper design, is always the optimal amount for any combination of input voltage, LED temperature, LED current and LED forward voltage variation.
However, problems always occur when the operating conditions are outside the normal window, for instance if a user plugs a 120 V LED lamp into a 220 V socket, the circuit inside the LED lamp may be damaged due to the over-voltage condition of the input voltage. Therefore, there is still a need to provide adequate safeguards to maintain product and user safety for operating under some abnormal conditions.